Microwave switch tube



March 21, 1967 J. D. WOERMBKE 3,310,706

MICROWAVE SWITCH TUBE Filed Feb. 6, 1964 INVENTOR, JAMES D. WOERMBKE.

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ATTORNEYS W F M United States Patent Ofifice 3,310,706 Patented Mar. 21, 1967 3,310,706 MICROWAVE SWITCH TUBE James D. Woermblte, Ellicott City, Md, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Filed Feb. 6, 1964, Ser. No. 343,167 9 Claims. (Cl. 315- 39) The present invention relates to a microwave switching device and more particularly to microwave switching devices for use with energy in the millimeter wavelength region.

In the field of radar, it has been the general practice to employ TR tubes to protect the sensitive receivers when both transmitter and receiver use a common antenna. As the frequency of operation of such microwave devices increases, the physical size of the component parts of the devices shrink in size. In the millimeter range of operation, the wavelengths are in the order of only a few tenths of an inch. When designing the standard millimeter microwave TR switch tubes the size of the parts prohibit easy fabrication. For example, the center electrode of the standard coaxial keep-alive structure would be only a few thousandths of an inch in diameter. Fabricating such a delicate electrode and then subse quently placing this electrode 'coaxially with respect to the standard conical electrode would require expensive equipment and great manufacturing skill. It is also noted that the center of the conical electrode would have to be machined out and an opening placed in the apex.

It is, therefore, the primary object of the present invention to provide a TR switch tube which may be relatively inexpensive and easily manufactured when designed for use in the millimeter wavelength region.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof, and wherein:

FIGURE 1 shows a perspective view, partly in section, of a preferred embodiment of the invention; and

FIG. 2 shows a section of the device taken on the line 2--2 of FIG. 1 looking in the direction of the arrows.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown a portion of a dual TR switch tube 11. It is pointed out that the invention, for purposes of illustration, is embodied in the dual switch tube. Of course, the invention is also useful in a single tube design as will be explained later.

Tube 11 comprises a waveguide section having broad walls 12, narrow walls 13 and a partition 14 which divides the waveguide into two equal compartments.

Disposed transversely within each compartment is a resonant structure comprising spaced, conical, capacitive electrodes 15 and 16 defining a discharge gap 17, an inductive plate 19, and an inductive matching structure in the form of a sleeve 20. Plate 19 and sleeve 20 define an iris 21 in which capacitive electrodes 15 and 16 are mounted.

A keep-alive structure comprising electrodes 23 and 24 which define a gap 25 is mounted in sleeve 20. Openings 26 are provided in sleeve 20 with gaps 17, gap 25, and openings 26 linearly disposed. Electrode 24 is connected directly to the waveguide wall 12 while electrode 23 extends through an opening 27 in the top wall 12 and is D.C. isolated from the waveguide. A dielectric structure, comprising insulating rings 28 and 29, and a collar 30 hermetic-ally seals the opening 27 and centers the electrode 23.

Each inductive plate 19 is provided with a bias electrode 31 insulated from plate 19 by a glass sleeve 32. Electrode 31 extends through wall 12 and into plate 19. A window 33 is provided in plate 19 opposite gap 17 where electrode 31 is exposed by removing a portion of glass sleeve 32.

The structure shown in FIGS. 1 and 2 is only that portion of the TR switch which comprises the discharge gap and the keep-alive structure. Obviously, many other resonant structures may be placed along the waveguide section while both ends of the section are hermetically sealed with any of the well-known resonant coupling windows. The entire assembly is filled with an ionizable gas of exact predetermined composition and pressure.

In operation, a negative DC. voltage is applied to the keep-alive electrode 23 so as to produce a gas discharge within the sleeve 20. Free electrons will then diffuse through the openings 26 and into the gap 17. These free electrons should provide sufi'icient residual ionization in the gap 17 sufiicient to produce an almost instantaneous discharge across gap 17 when a transmitter pulse occurs. A voltage is developed across the gap 17 by microwave energy in the waveguide. Energy coming directly from the transmitter will develop a high voltage across gap 17. This voltage will be sufiiciently high to completely ionize the gap 17, thereby destroying resonance at the iris 21 which will offer a very high impedance to the transmitted energy. Received energy which is relatively weak will not produce a voltage sufiiciently high to discharge the gap. In this case, the iris 21 offers little or no impedance to the passage of energy.

The bias electrodes 31 are provided to insure a partial ionization of gaps 17. By applying a positive bias voltage to the electrodes 31, an accelerating field for the free electrons in the region of the openings 26 is provided. This field will tend to draw the electrons into the gap 17 and thus increase the electron density in that area. The electron density and hence ignitor interaction will be a function of the keep-alive voltage and the positive bias voltage.

It can be seen that the sizes of the parts permits relatively easy fabrication. The region of the iris 21 is kept substantially free of any obstruction which could cause discontinuities. The keep-alive electrodes may be made relatively large, while the sleeve 20 can be easily designed and take on a diameter such as to be part of the microwave resonant structure. The distance between the gap 17 and the keep-alive electrodes or the opening 26 is not too far to present a diffusion problem for the free electron-s. In the millimeter wavelength region, the distance between the bias electrode 31 and the keep-alive structure is about 0.080 to 0.100 inch. The openings 26, gaps 17, and windows 33 are all in line so as to insure maximum electron density at the gap 17.

The structure shown in FIGS. 1 and 2 may be easily modified for use in a single tube design. All that need be done is to omit one of the sides, leaving the partition 14 and the sleeve 20 as the waveguide outer wall. Of course, one of the openings 26 would have to be omitted depending on which side is omitted.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A microwave switching device comprising: a sec tion of waveguide filled with an ionizable gas; means separating said section into a plurality of compartments; a resonant structure mounted in each said compartment; each said resonant structure including inductive means, de-

fining an iris, and capacitive means, defining a discharge gap, mounted in said iris; means mounted between said compartments for generating free electrons; and aperture means in the said inductive means of each said iris for permitting the direct fio'w of electrons from said generating means into'said discharge gaps.

, 2. The microwave switching device of claim 1 and further including: means providing a biasing voltage for increasing the flow of said electrons into said discharge l?- 3. The microwave switching device of claim 1 and wherein each said discharge gap, said means generating free electrons, and each said aperture means are all linearly disposed.

4. A microwave switching device comprising: a section of waveguide filled with an ionizable gas; a resonant structure mounted in said section; said resonant structure including a pair of inductive elements mounted on opposite sides of said section, and a pair of spaced capacitive electrodes mounted between said inductive elements defining a discharge "gap; one said inductive element being a sleeve having an opening in the wall thereof adjacent said discharge gap; and keep-alive electrode means mounted in said sleeve for generating free electrons,

5. The microwave switching device of claim 4 and further including a biasing electrode mounted in the other said inductive element.

6. The microwave switching device of claim 5 and wherein said biasing electrode, said discharge gap, and said opening are linearly disposed.

7. A microwave switching device comprising: a section of waveguide filled 'with an iionizable gas, means separating said section into a plurality of compartments; a resonant structure mounted in each said compartment; each said resonant structure including a pair of inductive elements mounted on opposite sides of said compartment, and a pair of spaced capacitive electrodes mounted between said inductive elements defining a discharge gap; said inductive elements mounted onvsaid separating means being a sleeve and extending into adjacent compa'ntments; a pair of openings provided in said sleeve, each opening communicating with one of said adjacent compartments; and keep-alive electrode means mounted in said sleeve "for generating free electrons.

8. The microwave switching device of claim 7 and further including a biasing electrode mounted in the inductive elements not containing said keep-aliveelectrode means.

9. The microwave switching device of claim 8 and wherein said biasing electrodes, said discharge gaps, and said openings are linearly disposed.

Reierences Cited by the Examiner UNITED STATES PATENTS 94637780 5/1953 Longacre 333--13 2,710,932 6/1955 Heins t 33313 FOREIGN PATENTS 771,369 4/1957 Great Britian. 1,044,638 6/1953 France.

DAV ID I. GALVIN, Primary Examiner. 

4. A MICROWAVE SWITCHING DEVICE COMPRISING: A SECTION OF WAVEGUIDE FILLED WITH AN IONIZABLE GAS; A RESONANT STRUCTURE MOUNTED IN SAID SECTION; SAID RESONANT STRUCTURE INCLUDING A PAIR OF INDUCTIVE ELEMENTS MOUNTED ON OPPOSITE SIDES OF SAID SECTION, AND A PAIR OF SPACED CAPACITIVE ELECTRODES MOUNTED BETWEEN SAID INDUCTIVE ELEMENTS DEFINING A DISCHARGE GAP; ONE SAID INDUCTIVE ELEMENT BEING A SLEEVE HAVING AN OPENING IN THE WALL THEREOF ADJACENT SAID DISCHARGE GAP; AND KEEP-ALIVE ELECTRODE MEANS MOUNTED IN SAID SLEEVE FOR GENERATING FREE ELECTRONS. 